1. Technical Field
This disclosure relates to an image forming apparatus, and more specifically to an image forming apparatus including a recording head for ejecting liquid droplets.
2. Description of the Related Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that uses a recording head (liquid-droplet ejection head) for ejecting droplets of ink.
Such an image forming apparatus may have, for example, replaceable main tanks (ink cartridges) and head tanks. The main tanks store different color inks to be supplied to one or more recording heads for ejecting ink droplets of different colors. The head tanks dedicated for the respective color inks receive the color inks from the main tanks and supply the inks to the recording heads.
Such an image forming apparatus may also have a maintenance unit (maintenance-and-recovery unit) to maintain and recover the performance of the recording heads. The maintenance unit typically has suction caps to cover the nozzle faces of the recording heads and a suction pump connected to the suction caps to suck ink from nozzles of the recording heads.
Furthermore, such an image forming apparatus may have an air release unit and an air release driving unit. The air release unit is disposed at the head tank and openable to release air from the interior of the head tank to the atmosphere. The air release driving unit is disposed at an apparatus body to drive the air release unit.
In a case where such an image forming apparatus has multiple pumps, such as liquid feed pumps and the suction pump, if multiple driving motors are provided as driving sources dedicated for the respective pumps, the size and cost of the image forming apparatus increases.
Hence, for example, JP-2003-145802-A proposes an image forming apparatus having a sun gear, a planet gear, pump driving gears, and a revolution regulation unit to selectively drive three or more pumps with a single driving source. The sun gear is rotated in first and second directions by the rotation drive force of a selective driving mechanism. The planet gear revolves around the sun gear with rotation of the sun gear and rotates on its axis with rotation of the sun gear when the revolution is restricted. The pump driving gears are arranged along the revolution trajectory of the planet gear to in turn engage the planet gear when the planet gear revolves with the rotation of the sun gear in the first direction. The revolution regulation unit restricts the revolution of the planet gear performed with the rotation of the sun gear in the second direction, at positions where the planet gear engages the pump driving gears.
However, the above-described configuration poses difficulties in activating the pumps independent of one another, as compared to a configuration in which dedicated driving sources for the respective pumps are employed. In addition, since the driving (rotation) direction of the pumps is limited to one direction, the above-described configuration has difficulties in being applied to, e.g., a case where liquid feed pumps for feeding liquid in both directions are used.